Pressure sensitive adhesives are well-known in the art and commonly used in adhesive systems such as tapes, decals, labels, transparent protective coverings, and the like. The adhesive systems typically comprise a laminate of an article, such as a label or paper tag having a coating of pressure sensitive adhesive on one side thereof, releasably adhered to a release sheet. The release sheet is usually a paper sheet coated or treated with a release material such as a wax or silicone. The release sheet is peelable from the label to expose the adhesive so that the label can be adhered to a supporting surface.
Labels capable of being removed from their applied surface are generally much more expensive than labels intended to bond permanently. In addition, the degree of removability is critical, i.e., too removable and it may fall off, or too permanent and it will not remove cleanly. It is therefore a great advantage if the bonding power of a single low cost adhesive can be tailored by modification to be removable from many different surfaces.
Furthermore, it is of great advantage for some uses to have discrete sections on a label with otherwise permanent adhesive performance to have varying degrees of removable performance. This can only be done now by such methods as coating two adhesives on the same web, laminating two separately coated materials together on the same liner, or coating different coat weights of the same adhesive in stripes to achieve varying performance.
Some articles and sheet materials are designed to be removed from one support surface and reapplied to another support surface. The high bonding power of pressure sensitive adhesives typically do not permit the article to be easily removed. To overcome the high bonding power of the pressure sensitive adhesive, a modified adhesive is used, having reduced tackiness, or the adhesive is replaced with a less tacky adhesive. This type of modification is more expensive than using a standard pressure-sensitive adhesive and makes it difficult to control adhesive bonding power of the adhesive in the finished article.
Several manufacturers have developed methods to control bonding strength of pressure-sensitive adhesives and the force required to separate the article from a support surface. One example as disclosed in British Patent No. 1,541,311, applies a non-continuous layer of beads of a polysiloxane material to a layer of a pressure sensitive adhesive during the initial manufacturing process. The release sheet is then laminated to the article to form a modified laminate that can be removed and repositioned. This system has the disadvantage that adhesive bonding properties of the laminate are determined by the manufacturing process and cannot be selectively modified by the user and cannot be modified subsequent to manufacture.
Another pressure sensitive adhesive system includes release dots on the adhesive material to prevent the adhesive from contacting the support surface. The material is applied to a support surface, and pressure is applied to extrude the adhesive around the dots. An example of this type of adhesive system is disclosed in U.S. Pat. No. 3,554,835 to Morgan. This adhesive system does not permit the article to be removed from the support surface or repositioned once the adhesive makes contact with the support surface.
Other pressure sensitive adhesive systems include a coated release sheet that enables the release sheet to be easily separated from the article. These release sheets may have the release coating applied in a selected pattern or include different release materials having different release properties. Examples of these adhesive systems are disclosed in U.S. Pat. No. 5,061,535 to Krechel et al. and U.S. Pat. No. 3,503,782 to Ayres, respectively.
The previous adhesive systems do not provide a means for modifying the bonding properties of a pressure sensitive adhesive after manufacture of the laminate. Thus, there is a continuing need for a pressure sensitive adhesive system having selected adhesive bonding strength that can be removed and repositioned on a support surface. This invention addresses this need as well as other needs in the art, which will become apparent to those skilled in the art once given this disclosure.